1. Field of the Invention
This invention relates to rotary kilns for the gasification of solid carbonaceous material such as described in copending patent application of P. G. Garside, Ser. No. 264,479 filed May 18, 1981, and U.S. Pat. No. 3,990,865 to Cybriwsky and Petersen dated Nov. 9, 1976. Particularly, this invention is directed toward a thrust containment device for maintaining kiln hoods in a stationary position during thermal expansion of kiln apparatus and while the kiln is operating at relatively high pressures.
2. Description of the Prior Art
As disclosed in the aforesaid copending patent application of P. G. Garside and U.S. Pat. No. 3,990,865, the gasification of coal can be attained in a pressurized rotary kiln. Such a kiln is equipped with stationary hoods at both ends of the kiln with seals connecting the hoods to the kiln shell. The seals may be of a type as disclosed in U.S. Pat. No. 4,087,334 to Harig et al dated May 2, 1978 so as to allow rotary motion of the kiln shell and accommodate axial and radial thermal expansion of the kiln shell while maintaining a gas-tight seal.
Rotary kilns for the commercial production of gas from coal are quite lengthy being of 250 feet or more in length and 12 feet or more in diameter. Additionally, such kilns operate at temperatures exceeding 2,000.degree. F. and pressures of up to 180 pounds per square inch greater than atmospheric pressure. Consequently, such kilns produce tremendous forces acting upon the hoods and seals of the kiln. Indeed, for a kiln operating at 75 pounds per square inch of pressure higher than ambient atmospheric pressure and having a seal diameter of 12 feet, axial forces acting upon the kiln hoods exceed 900,000 pounds.
These forces tend to urge the hoods out of alignment with the kiln shell resulting in undesirable displacement and reduction of kiln seal efficiencies. Indeed, I have determined that for a kiln with a seal diameter of ten feet, an angular displacement of as small as 1/32 inch is intolerable.
It has been suggested to maintain the kiln hoods in a stationary position by mounting them upon concrete foundations. However, the length of the kiln, the forces acting upon the hoods, and the slim tolerances permitted make traditional concrete foundations ineffective in most locations due to inadequate subsoil stability.
I have determined that tie members, or tie rods, connecting braces mounted upon the kiln hoods can be successfully employed to maintain kiln hoods in stationary positions during the kiln operation.
The use of tie members to relieve stresses resulting from pressure forces within a vessel are well known. For example, Illustrated Technical Dictionary, Vol. III, page 303, Brentano's Publishers, New York, New York (1908), illustrates the use of a tie rod to relieve stress between a steam boiler's walls. Also, Diesel Engineering Handbook, page 322, L. H. Morrison, Ed. (1939), illustrates the use of tie rods to secure cylinder heads in diesel engines. Tie rods are also known to have been used in constructing bridges and buildings.
However, the use of tie rods or tie members to control forces in a pressurized rotary kiln has, to my knowledge, never been attempted. Additionally, a tie rod assembly for such rotary kilns, due to a combination of the extreme length of the rods (e.g. 260 feet) and the extreme temperatures involved (e.g. 2,200.degree. F.), is prone to substantial thermal expansion. Also, the axial forces resulting from pressure inside the kiln (amounting to over 900,000 pounds) contribute to the expansion by reason of resulting tensile forces. Therefore, a tie rod assembly must overcome an expansion problem of unique magnitude not heretofore faced in applying tie rods to boilers, engines, bridges and buildings.
I have found this problem can be eliminated by providing the tie members with an expansion device, such as a bellows, to accommodate the expansion of the tie members while transmitting all pressure forces from the hoods to the tie members.
The object of the present invention is to provide a thrust containment device for a pressurized rotary kiln coal gasifier, to relieve forces from the kiln hood and seals.
It is a further object of the present invention to provide a thrust containment device for a pressurized rotary kiln gasifier employing tie members rigidly fixed to braces on either end of the kiln with an expansion means provided to accommodate thermal and tensile expansion of the tie members.